Plasma display panel

ABSTRACT

To provide a plasma display panel of improving a discharge time-lag. 
     A plasma display panel of the present invention is characterized in that it comprises a pair of substrate assemblies opposed to each other sandwiching discharge spaces formed to seal a discharge gas therein, wherein one of the pair of substrate assemblies comprises: display electrodes arranged on a substrate; a dielectric layer for covering the display electrodes; and a protective layer for covering the dielectric layer, and the protective layer is configured so that a plurality of MgO single crystals are adhered to an MgO film in such a manner that crystal orientations of the plurality of MgO single crystals are aligned in one direction.

TECHNICAL FIELD

The invention relates to a plasma display panel (hereinafter, referred to as PDP).

BACKGROUND ART

At the present, the type of AC-driven PDPs which are generally commercialized is the type of surface discharge PDP. In the type of surface discharge PDP, phosphor layers for color display can be positioned far away in the direction of the thickness of a display panel from a pair of display electrodes, so that the characteristic deterioration of the phosphors due to ion impact during discharging can be reduced. Thus, the type of surface discharge PDP is suitable for prolonging its life time rather than another type of opposed discharge PDP where a pair of display electrodes X and Y is formed to a front-side substrate and a rear-side substrate, respectively.

On a front-side substrate in the general type of AC-driven surface discharge PDP, a protective layer is provided for preventing a dielectric layer from being deteriorated by ion impact during discharging, the dielectric layer covering display electrodes X and Y. The protective layer not only prevents the dielectric layer from being deteriorated by ion impact during discharging, but also emits secondary electrons by ion impact thereto and provides a function to make discharge grow.

In general, the protective layer is employed as a thin film of magnesium oxide (MgO) considering high protection from ion impact and good emission capability of secondary electrons.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

As a protective film of the above-mentioned MgO has a high secondary electron emission coefficient, it is extremely effective to reduce a discharge start voltage. In order to meet a demand for a high-resolution display panel, however, it is necessary to further increase addressing speed, so that a problem of a discharge time-lag newly occurs. That is, it is a big problem how to shorten the discharge time-lag in order to perform a 1080-line scanning within a predetermined frame time period, by a sub-field scanning necessary for gradation display, according to the so-called full-high definition TV standard.

Herein, the discharge time-lag is generally considered to be a sum of a formative time-lag and a statistical time-lag. The formative time-lag is a time interval between the production of initial electron in the display electrodes and the formation of clear discharge, and is regarded approximately as the minimum discharge time when a number of discharges are produced. The statistical time-lag is a time interval between the application of a voltage to the occurrence of ionization up and the start of discharge, and is named because the statistical time-lag approximately causes variations in the case where a number of discharges are repeated. If these discharge time-lags are long, an address (write-in of a display) time also has to be long so as to avoid a mis-display, thereby causing a bad influence that actually a display time may be shorten. Therefore, it is desirable to make the discharge time-lag short.

As a possible solution to make the discharge time-lag short, conventionally, a technique that MgO single crystals are distributed on the MgO protective film has been proposed, for example, in Japanese Unexamined Patent Application Publication No. 2006-147417. However, conventionally, it has been difficult to uniform the characteristics of the respective panels. The improvement on this respect has been desired.

It is an object of the present invention to provide an improved panel structure for improving the discharge time-lag and, more particularly, to provide a new protective film structure for mass producing panels, with a high yield, whose characteristics are uniformed.

Means for Solving the Problems and Effects of the Invention

Briefly described, the principal idea of the invention is to scatter and distribute MgO single crystals on an MgO protective film in such a manner that the crystal faces of the MgO single crystals are aligned in a (100) crystal face.

More particularly, the present invention is characterized in that, in a plasma display panel having the MgO protective film on a dielectric layer covering electrodes, the surface of the MgO protective film has a (111) crystal face, and MgO single crystals having a (100) crystal face are uniformly scattered and distributed on the MgO protective film in such a manner that the (100) crystal faces of the MgO single crystals are parallel in unison to the surface of the MgO protective film, so as to partially cover the (111) crystal face of the MgO protective film.

Herein, it is important that a discharge surface exposed to a gas discharge space has both a superior initial electron emission function and a superior secondary electron emission function in order to improve the discharge time-lag, so that the underlying MgO protective film is therefore deposited in such a manner that their (111) crystal face is exposed so as to primarily have the secondary electron emission function, and the MgO single crystals are distributed on the MgO protective film in such a manner that the (100) crystal faces of the MgO single crystals are aligned in the direction of the surface of the MgO protective film so as to primarily have the initial electron emission function.

For the first time, an attention is paid by the present inventors that the MgO single crystals are distributed on the underlying MgO protective film so that particular crystal orientations of the MgO single crystals are aligned. In particular, in view of the particle diameters of the MgO single crystals and a coverage ratio of the MgO single crystals on the surface of the underlying MgO protective film, the improvements on the characteristics of the discharge surface are investigated to thereby lead to the present invention.

The adoption of the new discharge surface as above not only improves a discharge time-lag, but also characteristics of a manufactured panel can be uniformed because orientations of the MgO single crystals on the underlying MgO protective film are aligned at the (100) crystal faces. Further, since the contact between the surface of the underlying MgO protective film and the faces of the MgO single crystals is stable, problems of partial characteristic changes will not occur, caused by detached and/or removed MgO single crystals.

Hereinafter, various embodiments of the present invention will be exemplified.

The intensity of signals at a (200) crystal face after normalization may be the same as or more than the intensity of signals at a (111) crystal face per 1 μm of the MgO film, these signals being X-ray diffraction from the protective layer. In the case of the MgO single crystals, the diffraction signals at the (200) crystal face are equivalent with the diffraction signals at the (100) crystal face.

The plurality of MgO single crystals may have a grain size of 0.6 μm or more at 50% of a cumulative percentage in a grain size distribution.

The plurality of MgO single crystals may have a grain size at 10% of a cumulative percentage in a grain size distribution, which is 0.5 times or more of the grain size at 50% of a cumulative percentage.

The MgO single crystals may be adhered to the MgO film in such a manner that a changing rate of gloss levels at a measurement angle of 60 degrees will be 20-40%, the changing rate being measured before and after the MgO single crystals are adhered to the MgO film.

The various embodiments shown herein may be combined with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a configuration of PDP in accordance with an embodiment of the present invention.

FIG. 2 is an upside-down perspective view of a part of a front side of a substrate assembly shown in FIG. 1.

FIG. 3 is a graph showing X-ray diffraction pattern in an experiment for proving the effect of the present invention.

FIG. 4 shows a graph of a cumulative probability of discharge versus a discharge time-lag in the experiment for proving the effect of the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

-   1: front-side substrate assembly -   1 a: front-side substrate -   2X, 2Y: display electrodes -   3: dielectric layer of the front-side substrate -   4: protective layer -   4 a: MgO film -   4 b: MgO single crystals -   5: barrier ribs -   6R: red phosphor layers -   6G: green phosphor layers -   6B: blue phosphor layers -   7: dielectric layer of the rear-side substrate -   8: address electrodes -   9: rear-side substrate assembly -   9 a: rear-side substrate -   10: transparent electrode -   11: bus electrode

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described by use of the drawings. The contents shown in the drawings and the following description are exemplification, and the scope of the present invention is not limited to the contents shown in the drawings and the following description. Hereinafter, the present invention will be described taking an AC-driven three-electrode surface-discharge PDP for color display as an example.

1. PDP

A PDP in accordance with an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view illustrating a configuration of PDP in accordance with an embodiment of the present invention. FIG. 2 is an upside-down perspective view of a part of a front side of a substrate assembly shown in FIG. 1.

The PDP of this embodiment comprises a front-side substrate assembly 1 and a rear-side substrate assembly 9 opposed to each other sandwiching discharge spaces formed to seal a discharge gas.

The front-side substrate assembly 1 comprises, a plurality of display electrodes 2X and 2Y disposed on a front-side substrate 1 a, a dielectric layer 3 covering the plurality of display electrodes 2X and 2Y, and a protective layer 4 covering the dielectric layer 3, where the protective layer 4 is configured so that a plurality of MgO single crystals are adhered to an MgO film 4 a in such a manner that crystal orientations of the plurality of MgO single crystals 4 b are aligned in one direction.

The rear-side substrate assembly 9 comprises, a plurality of data electrodes 8 disposed on a rear-side substrate 9 a, a dielectric layer 7 covering a plurality of address electrodes 8 (also called to “data electrodes”), and barrier ribs 5 disposed on the dielectric layer 7 of two outsides of a address electrode 8, and a phosphor layer 6 formed on the surface of the dielectric layer 7 and both side surfaces of the barrier rids 5.

Hereinafter, each of constituent elements will be described in detail.

1-1. Front-Side Substrate, Display Electrodes, Dielectric Layer, Protective Layer (Front-Side Substrate Assembly)

A variety of the front-side substrate 1 a is not particularly limited. For example, the front-side substrate 1 a is a transparent substrate such as a glass substrate and the like.

In the inner side of the front-side substrate 1 a, there are arranged a plurality of display electrodes 2X and 2Y both horizontally extended and arranged in parallel. Each display line is a space between the neighboring display electrodes 2X and the display electrodes 2Y. This type of PDP is the so-called ALIS structure where the display electrodes 2X and 2Y are equally spaced and all regions between the neighboring electrodes 2X and 2Y become the display lines. The present invention, however, can be applied to another type of PDP where a pair of display electrodes 2X and 2Y is separated by a non-discharge interval (a non-discharge gap).

The display electrodes 2X and 2Y may be composed of a transparent electrode 10 made of materials such as ITO, SnO₂ and the like, and a metallic bus electrode 11 made of materials such as Ag, Au, Al, Cu, Cr, and laminates thereof (for example, a Cr/Cu/Cr laminate structure). The display electrodes 2X and 2Y may be formed by a thick film formation technique such as a screen printing method with respect to Ag and Au, and may be formed by a thin film formation technique such as a vapor deposition method or sputtering method, and an etching technique with respect to other metals, so that a predetermined number of display electrodes may be deposited in a predetermined thickness, wideness and interval. The transparent electrode 10 primarily contributes to a discharge activity, which is light transmitting for the user to see the light emission of the phosphor layer from the front-side substrate 1 a. It is preferable that the bus electrode 11 has a low resistance to be able to primarily conduct a current during discharging. Shapes of the transparent electrode 10 and the bus electrode 11 are not particularly limited, and a straight electrode, a T-electrode or a ladder shaped electrode may be employed. The shapes of the transparent electrode 10 and the bus electrode 11 may be similar to or different from each other. For example, the transparent electrode 10 may be the T-electrode or the ladder shaped electrode while the bus electrode 3 b may be the straight electrode.

The dielectric layer 3 is deposited for covering the display electrodes 2X and 2Y on the display electrodes 2X and 2Y. The dielectric layer 3 can be formed by applying a low melting point glass frit paste onto the front-side substrate 1 a by a screen printing method, and burning the frit paste. Also, the dielectric layer 3 can be formed by pasting a sheet-like dielectric layer and burning. Furthermore, the dielectric layer 3 may be formed by depositing silicon oxide (SiO₂) by a plasma CVD process.

The protective layer 4 is provided on the dielectric layer 3 for protecting the dielectric layer 3 from ion impact due to the discharge during displaying 3. The details of the protective layer 4 will be described later.

1-2. Rear-Side Substrate, Address Electrode, Dielectric Layer, Barrier Rib, Phosphor Layer (Rear-Side Substrate Assembly)

A variety of the rear-side substrate 9 a is not particularly limited. For example, the rear-side substrate 9 a is transparent substrates such as a glass substrate and the like.

On the inner side of the rear-side substrate 9 a, a plurality of address electrodes 8 are formed horizontally in the crossing direction with the display electrodes 2X and 2Y, and the dielectric layer 7 is formed for covering the data electrodes 8. The address electrodes 8 are provided for forming address discharges to select emission cells at the intersections between the address electrodes 8 and the display electrodes 2Y. The address electrodes 8 may be formed of, for example, a Cr/Cu/Cr laminate structure.

Otherwise, the address electrodes 8 may be composed of metals such as Ag, Au, Al, Cu, Cr and the like. Similarly as the display electrodes 2X and 2Y, the address electrodes 8 may be formed by a thick film formation technique such as a screen printing method with respect to Ag, and Au, and may be formed by a thin firm formation technique such as a vapor deposition method or sputtering method, and an etching technique with respect to other metals, so that a predetermined number of display electrodes may be deposited in a predetermined thickness, wideness and interval.

The dielectric layer 7 of the rear-side substrate can be formed with the same material and by the same method as in the dielectric layer 3 on the front-side substrate 1 a.

A plurality of barrier ribs 5 are formed on the dielectric layer 7 between the two neighboring address electrodes 8 for partitioning a discharge space. The shape of the barrier ribs 5 in this embodiment is a stripe. The shapes of the barrier ribs 5 may be meander shapes, lattice shapes or ladder shapes.

The barrier ribs 5 may be formed by a sandblasting method or a photo etching method. For example, the barrier ribs 5 can be formed in the sandblasting method by applying a frit paste composed of a glass frit having a low melting point, a binder resin and a solvent onto the dielectric layer 7, drying the frit paste, spraying cutting particles under the condition that a cutting mask having an opening of a pattern of barrier ribs is placed on this frit paste layer, cutting a frit paste layer exposed from the opening of the cutting mask, and further burning it. The barrier ribs 5 can be formed in the photo-etching method using a photosensitive resin as the binder resin and then exposure and development using a mask, and burning it, in place of cutting with the cutting particles.

At the sides and the bottom of the discharge space partitioned by the barrier ribs 5, phosphor layers 6R, 6G and 6B of red (R), green (G) and blue (B), respectively, are formed. The phosphor layers 6R, 6G and 6B can be formed by applying a phosphor paste containing a phosphor powder, a binder resin and a solvent to the discharge space partitioned by the barrier ribs 5 by a screen printing method or a method of using a dispenser, repeating this application for every color (R, G, B), and burning it.

It is possible that the phosphor layers 6R, 6G and 6B may be formed by using a sheet-like phosphor layer material (the so-called green sheet) containing a phosphor powder, a photosensitive material and a binder resin, and using a photolithography technique. In this case, a predetermined color sheet may be adhered to the display area of the substrate, and this may be light exposed and developed, repeatedly, by the number of the respective colors, so that the phosphor layers 6 of the respective colors may be formed between the corresponding barrier ribs 5.

The above-mentioned front-side substrate assembly 1 and rear-side substrate assembly 9 are confronted so that the display electrodes 2X and 2Y cross the address electrodes 8, and the surroundings are sealed to finalize a PDP by fulfilling a discharge gas containing a Ne gas as a main component and Xe within the discharge space surrounded by the barrier ribs 5. In this type of PDP, a discharge space at the intersections between the display electrodes (2X and 2Y) and the address electrodes 8, is a single cell (unit emission region) defined as a minimum unit of display. A single pixel comprises three cells of R, G and B.

1-3. Protective Layer

The protective layer 4 as the primary feature of the present invention will be next described in detail. The protective layer 4 is configured so that a plurality of MgO single crystals 4 b are adhered to an MgO film 4 a in such a manner that crystal orientations of the plurality of MgO single crystals 4 b are aligned in one direction.

The MgO film 4 a can be formed by a thin film formation process, known in this field, such as electron beam deposition method or sputtering.

The MgO single crystals 4 b may be made of MgO only or otherwise may contain a small amount of another ingredient (such as the residue of flux) in such an amount not to influence the crystal structure. The MgO single crystals 4 b are cubical crystals where all the crystal faces are equivalent with respect to the physical and chemical properties. Therefore, when the plurality of MgO single crystals 4 b are adhered on the MgO film 4 a so that any crystal surface of the MgO single crystals 4 b is adhered to the surface of the MgO film 4 a, the crystal orientations of the plurality of MgO single crystals 4 b are also aligned in one direction. In other words, the crystal orientations of the plurality of MgO single crystals 4 b are aligned in one direction unless obstacle such as fine grains interposed between the crystal surfaces of the MgO single crystals 4 b and the MgO film 4 a. The phrase, “the crystal orientations are aligned in one direction” means that directions of normal lines of crystal faces of cubical crystals are aligned in one direction. As long as the directions are aligned in one direction, it is no matter that the cubical crystals may be turned around the normal lines.

Here, microscopically, the surface of the underlying MgO film 4 a deposited by the electron beam deposition method has an uneven column crystal structure, and fine spaces between summits of column crystals. Therefore, if an interval between the summits is shorter than a diameter of the MgO single crystal to be adhered, the underlying MgO film can be substantially flat, so that the crystal orientations of the MgO single crystals will be conveniently aligned. In other words, if many MgO single crystals, whose diameter is shorter than twice of the interval between the summits of the column crystals of the underlying MgO film, are present, the MgO single crystals will tilt and slip into the fine spaces between the summits, and therefore the crystal orientations of the MgO single crystals will not be aligned.

In view of the above, according to the present invention, a grain size of the plurality of MgO single crystals 4 b at 50% of a cumulative percentage in a grain size distribution, is preferably 0.6 μm or more, and more preferably 0.9 μm or more. That is, as technical requirements to align the crystal orientations, it is necessary that the diameter of each of the MgO single crystals that occupy more than a half of a unit volume is 0.6 μm or more, and preferably 0.9 μm or more, and more preferably 1.3 μm or more. If the diameters are too small, as stated above, the edges of the MgO single crystals 4 b may slip into the fine spaces of the surface of the MgO film 4 a, so that, preferably, the diameters of the MgO single crystals being shorter than 0.1 μm are excluded. In addition, preferably, the grain size of the MgO single crystals 4 b at 50% of a cumulative percentage is 30 μm or less. If the diameters are too large, the exposure areas of the underlying MgO film having the secondary electron emission function become narrow to thereby increase the discharge voltage. The grain size distribution of the plurality of MgO single crystals 4 b can be measured using a particle size distribution analyzer of the laser diffraction type.

The grain size of the plurality of the MgO single crystals 4 b at 50% of a cumulative percentage in the grain size distribution may be specifically, for example, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 4, 5, 10, 15, 20, 25, or 30 μm. The grain size of the plurality of the MgO single crystals 4 b at 50% of a cumulative percentage may be in the range between any two of numerals exemplified above.

The grain size of the plurality of the MgO single crystals 4 b at 10% of a cumulative percentage in the grain size distribution is not particularly limited but, preferably, 0.5 times or more of the grain size at 50% of a cumulative percentage. In this case, a percentage of fine MgO single crystals in the plurality of MgO single crystals 4 b is low. The fine MgO single crystal is interposed between the crystal surface of larger MgO single crystal 4 b and the MgO film 4 a to thereby interfere the contact between the crystal surface of the MgO single crystal 4 b and the MgO film 4 a, so that the crystal orientations of the MgO single crystals 4 b are prevented from being aligned. If the grain size of the plurality of the MgO single crystals 4 b at 10% of a cumulative percentage is 0.5 times or more of the grain size at 50% of a cumulative percentage, the percentage of the fine MgO single crystals 4 b in the MgO single crystals is too low so that the alignment of the crystal orientations of the MgO single crystals 4 b is easy.

The grain size of the plurality of the MgO single crystals 4 b at 10% of a cumulative percentage in the grain size distribution may be specifically, for example, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95 times of the grain size at 50% of a cumulative percentage. The grain size of the plurality of the MgO single crystals 4 b at 10% of a cumulative percentage may be in the range between any two of numerals exemplified above or more than any one number exemplified above. As the grain size of the plurality of the MgO single crystals 4 b at 10% of a cumulative percentage is closer to the grain size of the plurality of the MgO single crystals 4 b at 50% of a cumulative percentage, the alignment of the crystal orientations of the MgO single crystals 4 b becomes easier.

Whether the crystal orientations of the plurality of MgO single crystals 4 b are aligned can be determined based on the ratio between the signal intensity at a crystal face of (200) and that at a crystal face of (111) using an X-ray diffraction (XRD). The crystal face of (200) of the MgO single crystals is equivalent with that of the crystal face of (100). The signal intensity at the crystal face of (200) is strong when the crystal orientations of the plurality of MgO single crystals 4 b are aligned and the signal intensity at the crystal face of (200) is very weak when the crystal orientations of the plurality of MgO single crystals 4 b are not aligned. On the other hand, the signals at the crystal face of (111) are primarily the signals from the MgO film 4 a and they rarely depend upon whether the crystal orientations of the plurality of MgO single crystals 4 b are aligned. Accordingly, the value of the ratio of {[the signal intensity at a crystal face of (200)] over [the signal intensity at a crystal face of (111)]} indicates whether the crystal orientations of the plurality of MgO single crystals 4 b are aligned or not. As an example, if the signal intensity at a crystal face of (200) after normalization is more than one time the signal intensity at the crystal face of (111) per 1 μm of the MgO film, it can be determined that the crystal orientations of the plurality of MgO single crystals 4 b are aligned. Here, the “normalization” means that a measured value of the signal intensity at a crystal face of (200) is multiplied by 0.116 with the signal intensity at the crystal face of (111) being a reference, considering that the ratio of the measured signal intensity between the crystal face of (200) and the crystal face of (111) is 11.6/100 when the existence ratio between the crystal face of (200) and the crystal face of (111) is 1/1.

The production method of the MgO single crystals 4 b is not particularly limited but, as an example, MgO seed crystals manufactured by a gas phase method and a small amount of flux (accelerant) are mixed and burned so that a burned product is then pulverized. Since the MgO seed crystals manufactured by the gas phase method are small in size and large in size variations, the crystal orientations of the MgO seed crystals cannot be aligned even if the MgO seed crystals manufactured by the gas phase method are as such scattered on the MgO film 4 a. On the other hand, the MgO single crystals 4 b manufactured above are large in size and small in size variations. Then, if the MgO single crystals 4 b manufactured above are scattered on the MgO film 4 a, the crystal orientations of the plurality of MgO single crystals 4 b can be aligned. The flux may be employed by a halide of magnesium (magnesium fluoride, etc.).

For example, burning is performed at the temperature of 1000 to 1700° C. for 1-5 hours. In general, the sizes of the MgO single crystals 4 b become larger as the burning temperature is higher, the burning period is longer, and the amount of the flux is more. Since the sizes of the MgO single crystals 4 b are smaller and the speed of the crystal growth during the burning is faster, the variations in the sizes of the MgO single crystals 4 b become smaller as the burning temperature is higher, the burning period is longer, and the amount of the flux is more. Thus, in order to be a desired grain size distribution of the MgO single crystals 4 b, the burning temperature, the burning period and the amount of the flux are suitably controlled. The burning temperature may be, for example, 1000, 1100, 1200, 1300, 1400, 1500, 1600 or 1700° C. The burning temperature may be in the range between any two of numerals exemplified above. The burning period may be, for example, 1, 2, 3, 4 or 5 hours. The burning period may be in the range between any two of numerals exemplified above. The amount of the flux may be, for example, 0.01-0.1 wt % and, specifically, for example, 0.001, 0.002, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1 wt %. The amount of the flux may be in the range between any two of numerals exemplified above. The method of pulverizing the burned product is not particularly limited but, as an example, the burned product is placed within a mortar to pulverize it with a pestle into powder.

The production of the MgO seed crystals by the gas phase method may be carried out specifically, for example, by a method described in Japanese Unexamined Patent Application Publication No. 2004-182521 and/or a method described in “Synthesis of Magnesia Powder by Gas Phase Method and Its Properties” in “Material” Vol. 36, No. 410, pp. 1157-1161, on November (1987). Further, the MgO seed crystals manufactured by the gas phase method may be bought from Ube Material Industries, Ltd.

A method of adhering the MgO single crystals 4 b to the MgO film 4 a is not particularly limited. As an example, the MgO single crystals 4 b dispersed in a disperse medium or the MgO single crystals without change may be applied or scattered to the MgO film 4 a, so that the MgO single crystals 4 b can be adhered to the MgO film 4 a. The application or scattering may be specifically performed, for example, by an electrospray deposition method, a spray method, a screen printing method, an offset printing method, a dispenser method, a roll coating method, a die coating method, a doctor blade method or an ink-jet method. Otherwise, after a paste containing the MgO single crystals 4 b may be applied on a support film, it may be dried to make a film of the MgO single crystals. The film of the MgO single crystals may be laminated on the MgO film 4 a. Thus, anyway, the MgO single crystals 4 b can be adhered to the entire regions or a portion of the MgO film 4 a.

The adherence amount of the MgO single crystals 4 b to the MgO film 4 a is not particularly limited but, as an example, it is preferable that the MgO single crystals are adhered to the MgO film in such a manner that a changing rate of gloss levels at a measurement angle of 60 degrees will be 20-40%, the changing rate being measured before and after the MgO single crystals are adhered to the MgO film. The changing rate of gloss levels is defined by the following formula.

changing rate (%) of gloss levels={1−(gloss level after the MgO single crystals 4b are adhered)/(gloss level before the MgO single crystals 4b are adhered)}×100

The gloss level can be measured by a glossmeter (for example, a handy glossmeter IG-331 manufactured by HORIBA, LTD.) The gloss level before the MgO single crystals 4 b are adhered can be considered to be equivalent with the gloss level at the surface of the MgO film after the once adhered MgO single crystals 4 b are removed.

As the adherence amount of the MgO single crystals 4 b is larger, the changing rate of gloss levels is also larger. Accordingly, the changing rate of gloss levels is a value for reflecting the adherence amount of the MgO single crystals 4 b. If the adherence amount of the MgO single crystals 4 b is too small, the problem may be that an effect to improve the discharge time-lag may be also small, and if the adherence amount is too large, the problem may be that the discharge voltage may be increased. In order to properly adjust the adherence amount of the MgO single crystals 4 b, therefore, it is preferable that the MgO single crystals are adhered to the MgO film in such a manner that a changing rate of gloss levels at a measurement angle of 60 degrees will be 20-40%, the changing rate being measured before and after the MgO single crystals are adhered to the MgO film. Specifically, the changing rate of gloss levels may be, for example, 20, 25, 30, 35 and 40%. The changing rate of gloss levels may be in the range between any two of numerals exemplified above.

It is in the case where the variations of the changing rate of gloss levels are large in a short distance that the variations of the changing rate of gloss levels within the PDP display area influence the display properties. Thus, preferably, the variations of the changing rate of gloss levels are made to be less than 10%/mm.

2. Experiment for Proving Effect of Present Invention

In the following experiment for proving an effect of the present invention, the improvement effect of discharge time-lag was investigated by comparing the discharge time-lag between one case where the MgO single crystals 4 b, whose crystal orientations are aligned, are adhered to the MgO film 4 a and the other case where the MgO single crystals 4 b are not adhered to the MgO film 4 a.

2-1. Method for Producing MgO Single Crystals

The MgO single crystals 4 b were prepared by the following method.

First, MgF₂ (produced by Furuuchi Chemical Corporation, purity: 99.99%) were added as a flux by 48 ppm to MgO seed crystals (produced by Ube Material Industries, Ltd., trade name: HIGH PURITY & ULTRAFINE SINGLE CRYSTAL MAGNESIA POWDER (2000A)). This powder was mixed and milled with a mortar and a pestle.

Next, after the mixture and the milling, the resulting mixture was burned at 1450° C. for 1 hour in the air.

Next, the burned substance was pulverized into powder with a mortar and a pestle to obtain the MgO single crystals 4 b.

Here, a grain size distribution of the obtained MgO single crystals 4 b was measured using a particle size distribution analyzer of the laser diffraction type (model: HELOS & RODOS, produced by SYSMPATEC INC). As a result, a grain size at 10% of cumulative percentage, a grain size at 50% of cumulative percentage and a grain size at 90% of cumulative percentage were 0.8 μm, 1.2 μm and 2.1 μm, respectively. The grain size at 10% of cumulative percentage was 0.67 times the grain size at 50% of cumulative percentage, so that it was evident that the obtained MgO single crystals 4 b contained a small amount of fine grains.

2-2. Method for Producing PDP

Next, a PDP where the plurality of MgO single crystals 4 b were adhered on the MgO film 4 a so that the crystal orientations of the plurality of MgO single crystals 4 b were aligned in one direction was prepared according to the following method. Another PDP where the plurality of MgO single crystals 4 b were not adhered on the MgO film 4 a was also prepared by the same methods and under the same conditions in order to utilize it for a comparative experiment in a discharge time-lag test described later.

2-2-1. General Outline

As shown in FIG. 1, a front-side substrate assembly 1 was prepared by forming display electrodes 2X and 2Y, a dielectric layer 3, and a protective layer 4 (a plurality of MgO single crystals 4 b were adhered on a MgO film 4 a so that the crystal orientations of the plurality of MgO single crystals 4 b were aligned in one direction) on a front-side substrate 1 a made of glass. Further, a rear-side substrate assembly 9 was prepared by forming address electrodes 8, a dielectric layer 7, barrier ribs 5, and phosphor layers 6G, 6B and 6R on a rear-side substrate 9 a made of glass. Next, a panel having internal air-tight discharge spaces was prepared by overlaying the front-side substrate assembly 1 on the rear-side substrate assembly 2 and sealing these assemblies at their peripheral portions with a sealing material. Next, after evacuating the air in the discharge spaces, a discharge gas was introduced into the discharge spaces to complete a PDP.

2-2. Method of Adhering the MgO Single Crystals 4 b to the MgO Film 4 a

The MgO single crystals 4 b were adhered to the MgO film 4 a according to the following method.

First, the MgO single crystals 4 b were mixed in the rate of 2 gram with respect to 1 liter with IPA (produced by KANTO CHEMICAL Co., Inc, for the electronics industry), and the resulting mixture was dispersed with an ultrasonic dispersing machine and thereby the agglomerated crystals were dispersed to prepare slurry.

Next, the above-mentioned slurry was spray-applied onto the MgO film 4 a with a coating spray gun, and then this coat was dried by blowing a dry air. This step was repeated by several times to adhere the MgO single crystals 4 b to the MgO film 4 a. The MgO single crystals 4 b were adhered to the MgO film 4 a so that the density of the MgO single crystals 4 b was 2 g per 1 m² of the film.

Before and after the MgO single crystals 4 b were adhered to the MgO film 4 a, the ratios of the signal intensity were measured using an X-ray diffraction (XRD). FIG. 3 shows a graph of the measurement results.

With reference to FIG. 3, before the MgO single crystals 4 b were adhered to the MgO film 4 a, the signals at a crystal face of (111) and at a crystal face of (222) were observed and after the MgO single crystals 4 b were adhered to the MgO film 4 a, the signals at a crystal face of (111), at a crystal face of (222) and, in addition, at a crystal face of (200) were observed. The signal intensity at the crystal face of (111) and at the crystal face of (222) was unchanged before and after the MgO single crystals 4 b were adhered to the MgO film 4 a. The signal intensity at the crystal face of (200) after normalization was 1.9 times the signal intensity at the crystal face of (111) per 1 μm of the MgO film. These results indicated that the crystal orientations of the plurality of MgO single crystals 4 b were aligned in one direction. Another measurement using the X-ray diffraction (XRD) was performed with respect to another PDP where the MgO seed crystals were adhered on the MgO film 4 a by the same method. As a result, the signal intensity at the crystal face of (200) was very small and the signal intensity at the crystal face of (200) after normalization was less than 0.5 times the signal intensity at the crystal face of (111) per 1 μm of the MgO film.

Before and after the MgO single crystals 4 b were adhered to the MgO film 4 a, the gloss level was measured to calculate the changing rate of gloss levels. The gloss level was measured using a glossmeter (a handy glossmeter IG-331 manufactured by HORIBA LTD.) at a measurement angle of 60 degrees. As a result, the changing rate of gloss levels was 30%. This value was considered to be about 6%, being converted into a coverage factor of the MgO single crystals 4 b on the surface of the MgO film 4 a.

2-3. Others

Other conditions are as follows.

Front-Side Substrate Assembly 1:

Width of the transparent electrodes 10: 270 μm

Width of the bus electrodes 11: 95 μm

Width of the discharge gap: 100 μm

The dielectric layer 3: formed by applying a glass paste having a low melting point and burning the paste, thickness: 30 μm

The MgO film 4 a: the MgO layer by electron beam evaporation, thickness: 1.1 μm

Rear-Side Substrate Assembly 9:

Width of the address electrodes 8: 70 μm

The dielectric layer 7: formed by applying a glass paste having a low melting point and burning the paste, thickness: 10 μm

Thickness of a portion of the phosphor layers 6G, 6B and 6R, directly above the address electrodes 8: 20 μm

Height of the barrier ribs 5: 140 μm Width at a top portion of the barrier ribs 5: 50 μm

Pitch of the barrier ribs 5: 360 μm

The discharge gas: Ne 96%-Xe 4%, 500 Torr

3. Discharge Time-Lag Test

Next, a discharge time-lag test was performed on each PDP produced. In a discharge time-lag test, when a voltage was applied to the address electrodes 8, an interval was measured between the time of the voltage application and the actual starting time of the discharge. The interval of time was measured by 1000 times. FIG. 4 shows the relationship between the discharge time-lag and the cumulative probability of the discharge.

FIG. 4 shows the results between one case where the plurality of MgO single crystals 4 b, whose crystal orientations were aligned, were adhered to the MgO film 4 a, and another case where the plurality of MgO single crystals 4 b were not adhered to the MgO film 4 a. With reference to FIG. 4, it is evident that the former case improves the discharge time-lag. This results indicates that a PDP comprising a protective layer 4 in which the plurality of MgO single crystals 4 b are adhered on the MgO film 4 a so that the crystal orientations of the plurality of MgO single crystals 4 b are aligned in one direction, improves discharge properties such as the discharge time-lag and provides good discharge properties.

In the embodiments described above, the invention is described by exemplifying the type of AC-driven three electrode surface-discharge PDP comprising a pair of display electrodes on a front-side substrate and address electrodes on a rear-side substrate, but the invention is not limited to such a type and can also be applied to another type of three electrode surface-discharge PDP comprising a pair of display electrodes and address electrodes on a front-side substrate, where the display electrodes are arranged on an insulator layer formed on the address electrodes, and a dielectric layer and a protective layer are provided on the display electrodes. In addition, the present invention can be applied to a further type of AC-driven two opposing electrode discharge PDP comprising a pair of display electrodes X and Y respectively formed on opposing substrates.

INDUSTRIAL APPLICABILITY

The present invention can reduce discharge failure due to a discharge time-lag and can enable PDP to be mass produced with a high yield. Therefore, the PDP according to the present invention provide good display at a low cost, advantageously. 

1. A plasma display panel which is characterized in that it comprises a pair of substrate assemblies opposed to each other sandwiching discharge spaces formed to seal a discharge gas therein, wherein one of the pair of substrate assemblies comprises: display electrodes arranged on a substrate; a dielectric layer for covering the display electrodes; and a protective layer for covering the dielectric layer, and the protective layer is configured so that a plurality of MgO single crystals are adhered to an MgO film in such a manner that crystal orientations of the plurality of MgO single crystals are aligned in one direction.
 2. The plasma display panel according to claim 1, wherein the intensity of signals at a (200) crystal face after normalization is the same as or more than the intensity of signals at a (111) crystal face per 1 μm of the MgO film, these signals being X-ray diffraction from the protective layer.
 3. The plasma display panel according to claim 1, wherein the plurality of MgO single crystals have a grain size of 0.6 μm or more at 50% of a cumulative percentage in a grain size distribution.
 4. The plasma display panel according to claim 1, wherein the plurality of MgO single crystals have a grain size at 10% of a cumulative percentage in a grain size distribution, which is 0.5 times or more of the grain size at 50% of a cumulative percentage.
 5. The plasma display panel according to claim 1, wherein the MgO single crystals are adhered to the MgO film in such a manner that a changing rate of gloss levels at a measurement angle of 60 degrees will be 20-40%, the changing rate being measured before and after the MgO single crystals are adhered to the MgO film.
 6. A plasma display panel having an MgO protective film on a dielectric layer covering an electrode, which is characterized in that a surface of the MgO protective film has a (111) crystal face; and MgO single crystals having a (100) crystal face are uniformly distributed on the MgO protective film in such a manner that the (100) crystal faces of the MgO single crystals are parallel in unison to the surface of the MgO protective film, so as to partially cover the (111) crystal face of the MgO protective film.
 7. The plasma display panel according to claim 6 which is characterized in that the MgO single crystals are uniformly distributed in such a manner that a crystal face opposite to the (100) crystal face of the MgO single crystals is in contact with the surface of the MgO protective film.
 8. The plasma display panel according to claim 2, wherein the plurality of MgO single crystals have a grain size of 0.6 μm or more at 50% of a cumulative percentage in a grain size distribution.
 9. The plasma display panel according to claim 2, wherein the plurality of MgO single crystals have a grain size at 10% of a cumulative percentage in a grain size distribution, which is 0.5 times or more of the grain size at 50% of a cumulative percentage.
 10. The plasma display panel according to claim 3, wherein the plurality of MgO single crystals have a grain size at 10% of a cumulative percentage in a grain size distribution, which is 0.5 times or more of the grain size at 50% of a cumulative percentage.
 11. The plasma display panel according to claim 2, wherein the MgO single crystals are adhered to the MgO film in such a manner that a changing rate of gloss levels at a measurement angle of 60 degrees will be 20-40%, the changing rate being measured before and after the MgO single crystals are adhered to the MgO film.
 12. The plasma display panel according to claim 3, wherein the MgO single crystals are adhered to the MgO film in such a manner that a changing rate of gloss levels at a measurement angle of 60 degrees will be 20-40%, the changing rate being measured before and after the MgO single crystals are adhered to the MgO film.
 13. The plasma display panel according to claim 4, wherein the MgO single crystals are adhered to the MgO film in such a manner that a changing rate of gloss levels at a measurement angle of 60 degrees will be 20-40%, the changing rate being measured before and after the MgO single crystals are adhered to the MgO film. 